The present invention relates to refrigerated superconductive magnets with thermal diode coil supports.
Conduction cooled superconductive magnets which rely on two stage cryocoolers rather than consumable cryogens for cooling of the type shown and claimed in U.S. Pat. No. 4,924,198 can take several days to cool down from ambient temperatures using just the cryocooler which is sized for steady state operation. The amount of sensible heat to be extracted from the magnet is large due to the large mass of the magnet particularly those which are used for whole body magnetic resonance imaging.
The cryocooler has a first stage which provides cooling at 40K to a thermal radiation shield and a second stage which provides cooling at 10K to the superconductive coils. The cooling capacity at the second stage is small, on the order of 2 to 5 watts, which is adequate for steady stage operation.
One previous approach to solve this problem is disclosed in U.S. Pat. No. 4,926,646 in which the two stage cryocooler is replaced during part of the cool down period by a precooler through which a cryogen is pumped such as liquid nitrogen which boils and cools the portion of the magnet normally cooled by the first and second stages of the cryocooler. The cryocooler is replaced and the cooling continues until operating temperatures are ready.
Another approach is shown in U.S. Pat. No. 4,926,657 in which cooling passageways are made in integral parts of the two stage cryocooler interface and are initially cooled by introducing a cryogen such as nitrogen which boils off cooling the magnet. The cryocooler is then operated to cool the magnet to operating temperatures.
Both of these approaches have the disadvantage of requiring liquid cryogen including the inherent problems of handling and storage. The refrigerated magnet does not require consumable cryogen for persistent operation.
It is an object of the present invention to provide a refrigerated magnet which can be more quickly cooled without requiring a larger cryocooler or the use of consumable cryogens.
It is another object of the present invention to provide a refrigerated magnet which can be more quickly cooled without removing the cryocooler.
It is still another object of the present invention to provide a refrigerated magnet which can be more quickly cooled which does not require the use of any moving parts.